If you want to get the last few MHz out of your memory, without an annoying fan noise, you have to get the MIPS RAM Freezer. It's easy to integrate them in your water cooling loop. But you have to think if it is worth it for your kind of memory. Some modules benefit greatly from cooling, others not at all.
You need to buy them only once and will be able to use them for a long time, they are compatible to DDR1 and DDR2. The latest information is that the manufacturers are going to use the same size of PCB for next-gen memory (Elpida DDR3)
If we had an Extreme Overclocking Award, The MIPS RAM Freezer would have got it. For People like me, who spend hours and hours to squeeze the last few MHz out of the memory, it's one of the best toys I've ever had in my hands.